1. Field of the Invention
This invention relates to a direction correcting device for a shield tunnelling machine having a shield body provided with a head portion and a tail portion following the head portion. More particularly, the invention relates to a device that corrects the excavating direction of the head portion relative to the tail portion.
2. Description of the Prior Art
As one direction correcting device for a shield tunnelling machine, Japanese Publication No. 6123356 discloses a device including four double-acting hydraulic jacks disposed around the axis of a tail portion at equal angular intervals, each jack having one end connected to a head portion and the other end connected to the tail portion.
In this known direction correcting device, four jacks are divided into two sets, with one set of jacks disposed above the horizontal line passing through the axis of the tail portion and the other set of jacks disposed below the above-mentioned horizontal line. When the one set of jacks are respectively extended (or contracted) and the other set of jacks are respectively contracted (or extended), the head portion is directed upward (or downward) relative to the tail portion. Alternatively, the four jacks are divided into two sets, with one set of jacks disposed leftward of the vertical line passing through the axis of the tail portion and the other set of jacks disposed rightward of the above-mentioned vertical line. When the one set of jacks are respectively extended (or contracted) and the other set of jacks are respectively contracted (or extended), the head portion is directed leftward (or rightward) relative to the tail portion.
As another direction correcting device, Japanese Patent Publication No. 61-47956 discloses a device including a rod, having one end connected to a head portion and the other end connected to a tail portion and being disposed on the vertical line orthogonal to the axis of the tail portion, and two hydraulic jacks, each jack having one end connected to the head portion and the other end connected to the tail portion and being disposed symmetrically about the above-mentioned vertical line.
In this known direction correcting device, when both jacks are respectively extended or contacted, the head portion is directed upward or downward relative to the tail portion. Also, when one jack is extended and the other jack is contracted, the head portion is directed leftward or rightward relative to the tail portion.
However, since the direction correcting device disclosed in Japanese Patent Publication No. 61-23356 requires four jacks, the structure, such as piping for fluid to operate the jacks, is complicated. Also, in the direction correcting device disclosed in Japanese Patent Publication No. 61-47956, since the rod and two jacks receive loads acting on the head portion and the tail portion in the advancing and direction correcting operations, large-sized jacks are needed.